The efficient production of hydrogen is not only critical to a number of industrial processes, but plays a key part in creating a clean and efficient hydrogen economy. The idea of a fuel cell, able to convert hydrogen into water and electricity, has been around for over a century. The fuel cell however, has been ineffective as a viable commercial power source because of inefficiencies in the production of hydrogen. Hydrogen can be produced by many different methods. Common methods of producing hydrogen are steam reformation (SR), highly reactive metals, reactive metals, electrolysis, and high temperature electrolysis (HTE).
Steam reformation (SR) is believed to be the most economical and commercially viable process that is presently available. At high temperatures (700-1100° C.) and in the presence of a metal-based catalyst, steam reacts with a hydrocarbon, such as methane, to yield carbon monoxide and hydrogen. For most hydrocarbons, including methane, temperatures in excess of 700° C. are necessary. Carbon monoxide produced in the SR reaction is poisonous to most fuel cells. The carbon monoxide may be processed in a water gas shift reaction (WGS), an organic reaction which combines carbon monoxide with steam to produce hydrogen. Unfortunately, the WGS does not consume all the carbon monoxide requiring the fuel cell to be periodically cleaned. The carbon monoxide can also be partially removed by scrubbing or pressure swing adsorption, both of which are costly.
Highly reactive metals may also be used to produce hydrogen from water. Examples of such metals include: lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr), beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), radium (Ra), aluminum (Al), silicon (Si), phosphorus, (P), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), yttrium (Y), zirconium (Zr), niobium (Nb), lanthanum (La), hafnium (Hf), tantalum (Ta) and gallium (Ga). These metals oxidize in the presence of water creating hydrogen. Unfortunately they cannot be efficiently reduced back to the original metal.
Reactive metals have a reactivity less than the highly reactive metals, but are much more capable of being reduced back to the original metal once oxidized. Examples of reactive metals include: germanium (Ge), iron (Fe), zinc (Zn), tungsten (W), molybdenum (Mo), indium (In), tin (Sn), cobalt (Co) and antimony (Sb). The reduction/oxidation of iron was used as the primary industrial method for manufacturing hydrogen during the 19th and early 20th centuries. At elevated temperatures, iron strips oxygen from water, leaving pure hydrogen. Excess water is required to maximize hydrogen production from a given amount of iron. After the hydrogen is produced, excess water is condensed leaving an uncontaminated hydrogen gas steam. The steam reduction/iron oxidation process produces hydrogen and wustite (FeO) and/or magnetite (Fe3O4). To regenerate the iron metal, carbon monoxide or carbon is used to capture the oxygen from the iron oxide, forming iron metal and carbon monoxide (CO) or carbon dioxide (CO2). Another method of reducing the iron oxide is smelting the iron oxide, which requires high temperature due to the high melting point of iron (1538° C.). Unfortunately, both these methods are inefficient and kinetically difficult.
Electrolysis is a simple way of producing hydrogen. In electrolysis, an electrical current is applied between a pair of inert electrodes immersed in water. The amount of electrical energy that must be used equals the change in Gibbs free energy of the reaction plus the losses in the system. The losses can (theoretically) be arbitrarily close to zero, so the maximum thermodynamic efficiency equals the Gibbs free energy change of the reaction divided by the enthalpy change.
High temperature electrolysis (HTE) may also be used to produce hydrogen at as high as twice the efficiently of simple room temperature electrolysis. HTE is more efficient than simple room temperature electrolysis because some of the energy is supplied as heat, which is cheaper than electricity, and because the electrolysis reaction is more efficient at higher temperatures. In fact, at 2500° C., an electrical current is unnecessary because water breaks down to hydrogen and oxygen through thermolysis. However, such temperatures are impractical. Proposed HTE systems operate at 100 to 850° C. HTE has been demonstrated in a laboratory, but not on a commercial scale. Unfortunately a significant amount of energy is lost in HTE electrolysis from the high pressures the water must be exposed to in order to maintain it as a liquid.
Therefore there exists a need for a more efficient method of producing hydrogen. An object of the following invention is for a continuous, self-renewing method of producing hydrogen, requiring only a supply of steam and electricity once started. A further object of the following invention is a method of producing hydrogen at temperatures above the boiling point of water, without having to maintain the reaction at higher pressures. Still yet another object of the following invention is a method of producing hydrogen with about a 30% increase in efficiency over HTE.